Fastening rotor blades in a turbomachine

ABSTRACT

The rotor blades of a turbomachine are fastened to the rotor ( 3 ) of the machine by means of blade roots ( 1 ) by the blade roots ( 1 ) being anchored in peripheral grooves ( 2 ). According to the invention, the blade roots ( 1 ) have at least one recess or opening ( 4 ), which extends in the peripheral direction and in each of which a connecting piece ( 5 ) is arranged. This connecting piece ( 5 ) connects at least two blade roots ( 1 ) to form a blade pack. By means of the connection, the blade roots ( 1 ) are secured against twisting and falling out of the peripheral groove ( 2 ). The connecting piece ( 5 ) consists of a shaped piece, which is laid with little clearance into the recess or opening ( 4 ), a displacement of a blade root ( 1 ) and of the connecting piece ( 5 ) relative to one another still being possible. The blade root of the last blade of a blade row which is assembled in a peripheral groove is locked to the adjacent blade roots by a final connecting piece.

[0001] The invention relates to rotor blades with blade roots, which are fastened in peripheral grooves on the rotor of a turbomachine. It relates, in particular, to fastening them and securing them against twisting and falling out of the groove.

[0002] A known way of assembling rotor blades on a rotor of a turbomachine is anchoring by means of blade roots in T-shaped peripheral grooves. In order to permit the assembly of the blades in a peripheral groove, in particular the last blades, a certain assembly clearance in the peripheral direction is necessary. During operation of the machine, it can happen that the rotor blades are displaced and a gap forms which is large enough for a blade root to rotate and fall out of the groove. This problem is solved by reducing the assembly clearance by tightly fitting intermediate pieces between the blade roots so that the assembly clearance is filled up. After fitting of the intermediate pieces, however, the remaining clearance between the blade roots is often too small to permit free thermal expansions. Because of the expansions, forces then occur which can interfere with the smooth running of the rotor and finally cause vibrations.

[0003] The object of the invention is, therefore, to provide a fastening arrangement for rotor blades with blade roots in peripheral grooves on the rotor of a turbomachine, which arrangement prevents the blade roots from twisting and falling out and, at the same time, ensures a sufficiently large clearance for free thermal expansions.

[0004] This object is achieved by means of a blade fastening arrangement in accordance with claim 1. The blade roots, which are anchored in peripheral grooves, each have, according to the invention, at least one recess or opening which extends in the peripheral direction and in each of which is arranged a connecting piece which connects at least two blade roots to one another to form a blade pack. Thereby the blade roots connected in this way are prevented from twisting. A connecting piece consists of a shaped piece of an arbitrary cross section and it is arranged in a recess or opening whose cross section is matched to the shaped piece. In this arrangement, the recess or opening and the shaped piece are dimensioned in such a way that the shaped piece lies with little clearance in the recess or opening and that a displacement of a blade root and of the shaped piece relative to one another is still possible.

[0005] According to the invention, the rotational freedom of the blade roots about the blade longitudinal axis is reduced by the connection of blade roots to such an extent that they are secured against twisting and falling out. Intermediate pieces are fitted between the blade roots in order to partially fill up the assembly gap. They no longer, however, incorporate the function of securing the blade roots against twisting and they do not now need to be so tightly fitted. By this means, free thermal expansion of the blade roots is ensured.

[0006] In a first embodiment of the invention, the connecting piece consists of a shaped piece of rectangular cross section, which is laid into a similarly rectangular recess on the surface of the blade root which faces toward the rotor and bottom of the groove. In a second embodiment of the invention, the connecting piece consists of a round wire, which is pushed into a bore opening in the blade root. Here again, the diameter of the opening and that of the wire are dimensioned in such a way that a displacement of the blade root along the wire is possible.

[0007] In one variant, each of the blade roots has a recess or opening which extends in the peripheral direction. In a further variant of the invention, each of the blade roots has two recesses or openings, which extend parallel to one another in the peripheral direction and into each of which a connecting piece is laid or pushed.

[0008] In consideration of the thermal expansions of the turbine parts and assembly of the blade roots, various lengths of the connecting piece can be embodied. In one embodiment, there is an arrangement of a single connecting piece for this purpose, which connecting piece extends over almost the complete periphery of a groove and connects almost all the blade roots in this groove to one another. In a further embodiment, shorter connecting pieces are arranged in the recesses or openings, each of which connecting pieces connects two or more adjacent blade roots together to form a blade pack.

[0009] In a further embodiment with two recesses or openings extending parallel to one another, there is an arrangement of short connecting pieces, each of which connect two blade roots to one another to form a blade root pair. Connecting pieces which are arranged adjacent and parallel to one another are then offset by one blade root relative to one another, a first connecting piece being laid into a first recess or opening and connecting a first blade root and an adjacent, second blade root. A second, parallel connecting piece is laid into the second, adjacent recess or opening and connects the second blade root and the adjacent, third blade root, and so on.

[0010] The root of the last blade is rotated into an assembly gap provided for it in the groove and, to secure it against twisting, is locked to the adjacent blade roots by a final connecting piece, by a connecting piece being pulled into the recess or opening of the last blade root.

[0011] In a further embodiment of the blade fastening arrangement according to the invention, a contact pressure spring is arranged in each recess on the surface of the blade root facing toward the bottom of the groove, which contact pressure spring further reduces a displacement of the blade on the rotor so that a gap formation, and aerodynamic disadvantages resulting from it, are avoided.

[0012] In order to realize the fastening arrangement according to the invention, work is only necessary on the blade roots, whereas the rotor remains unaltered. This fastening arrangement is therefore particularly suitable for retrofitting to existing machines.

[0013]FIG. 1 shows a longitudinal section through a blade root which is anchored in a peripheral groove with a connecting piece according to the invention,

[0014]FIG. 2 shows a view II of a plurality of blade roots and an example of securing against twisting by connecting a plurality of adjacent blade roots,

[0015]FIG. 3 shows, in the same view as that of FIG. 2, a further example of securing against twisting according to the invention, by connecting a plurality of blade roots,

[0016]FIGS. 4a-e show, in the same view as that of FIG. 2, a procedure for assembling and locking the last blade root with connecting pieces according to the invention.

[0017]FIG. 1 shows a blade root 1, which is anchored in an inverted T-shaped peripheral groove 2 in a rotor 3 of a turbomachine. On the surface facing toward the bottom of the groove, the blade root 1 has a recess 4 with a rectangular cross section. A connecting piece 5 with a similarly rectangular cross section is laid into the recess with a small clearance. The cross section of the recess in the blade root and of the associated connecting piece is, fundamentally, arbitrary. Elliptical or round shapes, for example, can also be embodied instead of the rectangular cross section for the recess and the connecting piece. A round recess 6, in which there is laid a pressure spring 7 which additionally prevents displacements of the blade root, is arranged in the center of the surface of the blade root facing toward the bottom of the groove. FIG. 2 shows a view II of a plurality of adjacent blade roots 1, which are anchored in the peripheral groove and which are connected by a connecting piece 5. They form a pack of blade roots which, because of its larger length, cannot twist in the peripheral groove even if an assembly gap occurs due to displacement of the blade roots during operation. The connecting piece therefore ensures securing against twisting and this makes it impossible for the blades to fall out. In this way, the blade roots along the total periphery of the groove are connected to one another to form a plurality of such blade root packs. A connection of almost all the blade roots, with the exception of the last or the last two blades, by means of a single connecting piece can likewise be embodied.

[0018]FIG. 3 shows a plurality of blade roots anchored in a peripheral groove by means of a further arrangement, according to the invention, of connecting pieces. On their side facing toward the bottom of the groove, the blade roots 1, 1 a, 1 b, 1 c, 1 d each have two parallel recesses, which are arranged on both sides of the center of the blade root. Short connecting pieces 5 a, 5 b, 5 c are laid in both recesses. Each connecting piece connects one pair of blade roots, the connecting pieces arranged parallel and adjacent to one another being respectively offset by one blade root. A connecting piece 5 a is, for example, laid into the first recess of the two blade roots 1 a and 1 b, connecting them and securing them against twisting. A second connecting piece 5 d is laid into the second parallel recess of the blade roots 1 b, 1 c so that it connects this pair of blade roots. The next connecting piece 5 c is, in turn, laid into the recess on the first side of the blade roots and connects the blade roots 1 c and 1 d. The assembly of the last blade of the peripheral groove and the locking of its blade root to the adjacent blade roots by means of the connecting pieces according to the invention is shown in FIGS. 4a to 4 e. FIG. 4a shows blade roots 11 and 12, which are located at a distance from the blade roots 13 and 14 due to an assembly gap in the peripheral groove 2. The blade roots 11 and 12 are connected to one another by connecting pieces 5 d and 5 e. They both extend, for example, over a plurality of blade roots. The blade roots 13 and 14 are connected to one another and secured by means of connecting pieces 5 f and 5 g. FIG. 4b shows the same peripheral groove 2 with the last blade, whose blade root 15 has been anchored in the assembly gap of the groove 2. The recesses 4 of the blade root 15 are still empty in this case and the blade root is, therefore, not yet secured against twisting. The locking of this last blade root takes place as follows, in accordance with FIGS. 4c-e: the blade root 12 is first pushed over the remaining gap close to the blade root 15 so that the ends of the connecting pieces 5 d and 5 e become visible. The connecting piece 5 d is then pulled in the same direction until its end comes to rest in the recess 4 of the blade root 12. The assembly and locking is completed by the gaps between all the blade roots in the peripheral groove being slightly increased so that the gap which has remained after the assembly of the last blade is distributed over the complete peripheral groove. These remaining gaps are filled by means of intermediate pieces. The result is that almost all the blade roots are secured against twisting by two parallel-extending connecting pieces and the remaining blade roots are at least secured by one connecting piece. This ensures that none of the blades can twist and fall out of the groove. The intermediate pieces are a known component and are not shown here. They are dimensioned in such a way that they reduce the assembly clearance and, during operation of the turbine, no larger gap can form which could interfere with the smooth-running of the rotor. Because of the arrangement for securing against twisting, however, they no longer need to fill the assembly clearance completely, so that a sufficiently large free space, in which thermal expansions can be freely ensured, remains between the blade roots.

List of Designations

[0019]1, 1 a-1 d, 11-15 Blade root

[0020]2 Peripheral groove

[0021]3 Rotor

[0022]4 Recess

[0023]5, 5 a-g Connecting piece

[0024]6 Recess

[0025]7 Contact pressure spring 

1. A fastening arrangement for rotor blades on the rotor (3) of a turbomachine, the rotor blades each having a blade root (1) which is anchored in a peripheral groove (2), characterized in that the blade roots (1) each have at least one recess (4) or opening, the recess or opening extending in the peripheral direction, and in that a connecting piece (5), which is matched to the shape of the recess (4) or opening, is arranged in each recess or opening, and in that the connecting piece connects at least two blade roots (1) to form a blade root pack.
 2. The fastening arrangement for rotor blades as claimed in claim 1 , characterized in that the blade roots (1) each have two recesses (4) or openings, in each of which a connecting piece is arranged.
 3. The fastening arrangement for rotor blades as claimed in claim 1 or 2 , characterized in that the at least one recess (4) is respectively arranged on the side of the blade root (1) facing the bottom of the groove of the peripheral groove (2) and has a rectangular cross section, and in that the connecting piece (5), which is laid in each case into the at least one recess (4), is a shaped piece of the same rectangular cross section.
 4. The fastening arrangement for rotor blades as claimed in claim 1 or 2 , characterized in that the opening on the blade root (1) is a bore opening and in that the connecting piece consists of a wire of the same diameter which is pushed into the bore opening.
 5. The fastening arrangement for rotor blades as claimed in one of claims 1 to 4 , characterized in that the connecting pieces (5) extend over almost the complete periphery of the groove and connect almost all the blade roots (1) to form one blade pack.
 6. The fastening arrangement for rotor blades as claimed in one of claims 1 to 4 , characterized in that the connecting pieces (5) extend over two or more blade roots (1) and connect the latter to form a plurality of blade packs.
 7. The fastening arrangement for rotor blades as claimed in claim 6 , characterized in that each of the blade roots (2) has two recesses (4) or openings and the connecting pieces (5) each extend over two blade roots (1) and in that the connecting pieces, which are arranged parallel to one another, are arranged offset by one blade root.
 8. The fastening arrangement for rotor blades as claimed in one of claims 1 to 7 , characterized in that each of the blade roots (1) has a round recess (6) in which a contact pressure spring (7) is arranged.
 9. The fastening arrangement for rotor blades as claimed in one of claims 1 to 7 , characterized in that the last blade root (1) assembled into the peripheral groove (2) is locked to the adjacent blade roots by displacing one or two connecting pieces (5 d, 5 e). 